I found this article on TechRepublic while searching for just such a tutorial! I have put it here for my (and your) reference!
Takeaway: E-mail has become a mission-critical tool in most businesses. See how Nslookup and Telnet can help diagnose problems when e-mail doesn’t go through.
I love clean log files. Not only does it indicate a smooth running Exchange Server, but it makes it easy to spot errors. There has been a warning that appears every so often in the Exchange Server Application Event Log;
Event Type: Error
Event Source: Userenv
Event Category: None
Event ID: 1524 Description:
Windows cannot unload your classes registry file - it is still in use by other applications or services. The file will be unloaded when it is no longer in use.
Found the MSKB post that is supposed to take care of the issue.
http://support.microsoft.com/kb/837115
Installed the UPHClean utility. Back to clean logs!
TC